I'm trying to compare the performance numbers of the 915 and 916 options in the latest 3.2 version of the POH, but I'm confused. The numbers are given as % power, which is confusing since those aren't going to be the same powers for the two engines. But more importantly, the 916 tables don't make sense.
There's a column in the speed and range tables labeled "95%" with a footnote saying "max continuous power". But max continuous power for the 916 is 137hp and max power is 160hp, so max continuous is 85%. Furthermore, if we compare the cruise speeds tables at, say, 75% power, they are the same (actually, the 916 is one knot slower). That doesn't make sense, because 75% power for the 915 is 0.75*139.5 or 105hp. For the 916, 75% power should be 0.75*160 or 120hp. It can't be the case that the 916-equipped plane goes a knot slower with 15 extra horsepower.
It's also very strange that the climb numbers, which supposedly are stated for Vy at max continuous power, are 800fpm for the 915 and 940fpm for the 916. That's a 17% increase, but the difference in max continuous power is only 2hp or 2%. Maybe the MT prop is that much more efficient but, if so, why are the cruise speeds at max continuous power the same?
There must be something incorrect in how power the figures are reported. #slingsupport care to comment?
POH 916 performance figures don't make sense
POH 916 performance figures don't make sense
Blog of various projects: https://blog.familjenjonsson.org/blog/
-
TSiDreamer
- Posts: 4
- Joined: Tue May 21, 2024 9:33 am
- Location: Northern Colorado
Re: POH 916 performance figures don't make sense
Hi Lutorm,
I looked at the power figures for the two engines using the Rotax Operators Manuals. Although I get slightly different numbers, I agree with what you have to say. Using the Rotax numbers, the power figures at ISA standard temperature and pressure (15°C & 1013mB): 915iA C24 vs 916iA C24
5 Minute Max Power @ 5800rpm | 100% Throttle = 104 kW(139.4 hp) vs 100% Throttle = 117kW(156.8 hp) both at 100% power
Max Cont Power @ 5500rpm | 100% Throttle = 99.17 kW(132.9 hp) = 95% power vs 98.7% Throttle = 101 kW(135.4 hp) = 86% power.
To me, the most remarkable aspect of the 916 is its fuel efficiency. At max continuous power, the 916 produces 2.5 hp more than the 915 but it consumes 11.8% less fuel to do so. That works out to 36 minutes greater endurance with 50gal of fuel and likely over 100nm additional range!
As for the POH inconsistencies, we may need to wait for one of our fellow builders to give us some real numbers gleaned from their flight testing.
Mike
I looked at the power figures for the two engines using the Rotax Operators Manuals. Although I get slightly different numbers, I agree with what you have to say. Using the Rotax numbers, the power figures at ISA standard temperature and pressure (15°C & 1013mB): 915iA C24 vs 916iA C24
5 Minute Max Power @ 5800rpm | 100% Throttle = 104 kW(139.4 hp) vs 100% Throttle = 117kW(156.8 hp) both at 100% power
Max Cont Power @ 5500rpm | 100% Throttle = 99.17 kW(132.9 hp) = 95% power vs 98.7% Throttle = 101 kW(135.4 hp) = 86% power.
To me, the most remarkable aspect of the 916 is its fuel efficiency. At max continuous power, the 916 produces 2.5 hp more than the 915 but it consumes 11.8% less fuel to do so. That works out to 36 minutes greater endurance with 50gal of fuel and likely over 100nm additional range!
As for the POH inconsistencies, we may need to wait for one of our fellow builders to give us some real numbers gleaned from their flight testing.
Mike
-
TSiDreamer
- Posts: 4
- Joined: Tue May 21, 2024 9:33 am
- Location: Northern Colorado
Re: POH 916 performance figures don't make sense
Hi Lutorm,
I looked at the power figures for the two engines using the Rotax Operators Manuals. Although I get slightly different numbers, I agree with what you have to say. Using the Rotax numbers, the power figures at ISA standard temperature and pressure (15°C & 1013mB): 915iA C24 vs 916iA C24
5 Minute Max Power @ 5800rpm | 100% Throttle = 104 kW(139.4 hp) vs 100% Throttle = 117kW(156.8 hp) both at 100% power
Max Cont Power @ 5500rpm | 100% Throttle = 99.17 kW(132.9 hp) = 95% power vs 98.7% Throttle = 101 kW(135.4 hp) = 86% power.
To me, the most remarkable aspect of the 916 is its fuel efficiency. At max continuous power, the 916 produces 2.5 hp more than the 915 but it consumes 11.8% less fuel to do so. That works out to 36 minutes greater endurance with 50gal of fuel and likely over 100nm additional range!
As for the POH inconsistencies, we may need to wait for one of our fellow builders to give us some real numbers gleaned from their flight testing.
Mike
Edit 11/4: I created a table comparing fuel Flow for the 915is vs. the 916iS at various power setting in an attempt to make some sense of the flight manual performance figures.
I looked at the power figures for the two engines using the Rotax Operators Manuals. Although I get slightly different numbers, I agree with what you have to say. Using the Rotax numbers, the power figures at ISA standard temperature and pressure (15°C & 1013mB): 915iA C24 vs 916iA C24
5 Minute Max Power @ 5800rpm | 100% Throttle = 104 kW(139.4 hp) vs 100% Throttle = 117kW(156.8 hp) both at 100% power
Max Cont Power @ 5500rpm | 100% Throttle = 99.17 kW(132.9 hp) = 95% power vs 98.7% Throttle = 101 kW(135.4 hp) = 86% power.
To me, the most remarkable aspect of the 916 is its fuel efficiency. At max continuous power, the 916 produces 2.5 hp more than the 915 but it consumes 11.8% less fuel to do so. That works out to 36 minutes greater endurance with 50gal of fuel and likely over 100nm additional range!
As for the POH inconsistencies, we may need to wait for one of our fellow builders to give us some real numbers gleaned from their flight testing.
Mike
Edit 11/4: I created a table comparing fuel Flow for the 915is vs. the 916iS at various power setting in an attempt to make some sense of the flight manual performance figures.